<button id="btn">
  Button
</button>
<style>
/* From Uiverse.io by zjssun - Tags: button, neon */
button {
  padding: 10px 20px;
  text-transform: uppercase;
  border-radius: 8px;
  font-size: 17px;
  font-weight: 500;
  color: #ffffff80;
  text-shadow: none;
  background: transparent;
  box-shadow: transparent;
  border: 1px solid #ffffff80;
  transition: 0.5s ease;
  user-select: none;
}

#btn:hover,:focus {
  color: #ffffff;
  background: #008cff;
  border: 1px solid #008cff;
  text-shadow: 0 0 5px #ffffff,
              0 0 10px #ffffff,
              0 0 20px #ffffff;
  box-shadow: 0 0 5px #008cff,
              0 0 20px #008cff,
              0 0 50px #008cff,
              0 0 100px #008cff;
}
</style>
